A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents

A61F2/02—Prostheses implantable into the body

A61F2/30—Joints

A61F2002/30001—Additional features of subject-matter classified in A61F2/28, A61F2/30 and subgroups thereof

A61F2002/30316—The prosthesis having different structural features at different locations within the same prosthesis; Connections between prosthetic parts; Special structural features of bone or joint prostheses not otherwise provided for

A61F2002/30317—The prosthesis having different structural features at different locations within the same prosthesis

A61F2002/30327—The prosthesis having different structural features at different locations within the same prosthesis differing in diameter

A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents

A61F2/02—Prostheses implantable into the body

A61F2/30—Joints

A61F2/3094—Designing or manufacturing processes

A61F2/30942—Designing or manufacturing processes for designing or making customized prostheses, e.g. using templates, CT or NMR scans, finite-element analysis or CAD-CAM techniques

A61F2002/30957—Designing or manufacturing processes for designing or making customized prostheses, e.g. using templates, CT or NMR scans, finite-element analysis or CAD-CAM techniques using a positive or a negative model, e.g. moulds

A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents

A61F2/02—Prostheses implantable into the body

A61F2/30—Joints

A61F2/3094—Designing or manufacturing processes

A61F2/30942—Designing or manufacturing processes for designing or making customized prostheses, e.g. using templates, CT or NMR scans, finite-element analysis or CAD-CAM techniques

A61F2002/30957—Designing or manufacturing processes for designing or making customized prostheses, e.g. using templates, CT or NMR scans, finite-element analysis or CAD-CAM techniques using a positive or a negative model, e.g. moulds

A61F2002/30958—Designing or manufacturing processes for designing or making customized prostheses, e.g. using templates, CT or NMR scans, finite-element analysis or CAD-CAM techniques using a positive or a negative model, e.g. moulds using lost patterns, e.g. lost wax

A61F2/00—Filters implantable into blood vessels; Prostheses, i.e. artificial substitutes or replacements for parts of the body; Appliances for connecting them with the body; Devices providing patency to, or preventing collapsing of, tubular structures of the body, e.g. stents

A61F2/02—Prostheses implantable into the body

A61F2/30—Joints

A61F2/3094—Designing or manufacturing processes

A61F2/30942—Designing or manufacturing processes for designing or making customized prostheses, e.g. using templates, CT or NMR scans, finite-element analysis or CAD-CAM techniques

A61F2002/30962—Designing or manufacturing processes for designing or making customized prostheses, e.g. using templates, CT or NMR scans, finite-element analysis or CAD-CAM techniques using stereolithography

A61F2250/00—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof

A61F2250/0014—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof having different values of a given property or geometrical feature, e.g. mechanical property or material property, at different locations within the same prosthesis

A61F2250/0039—Special features of prostheses classified in groups A61F2/00 - A61F2/26 or A61F2/82 or A61F9/00 or A61F11/00 or subgroups thereof having different values of a given property or geometrical feature, e.g. mechanical property or material property, at different locations within the same prosthesis differing in diameter

Abstract

The invention concerns a bone substitute with controlled anatomical shape and macroporous structure made from chemically consolidated cement phosphocalcic materials. Said substitute can be obtained by forming a liquid or plastic paste consisting of calcium phosphate and other hardly soluble calcium salts. The forming by moulding used with a paste and its chemical consolidation ex-vivo enables to obtain a substitute having a more or less large size whereof the controllable anatomical shape corresponds to that of the bone block to be replaced, and an adapted macroporous architecture promoting rehabitation and resorption of the substitute, while ensuring the best initial mechanical properties and their being preserved until the graft is definitely replaced by the newly formed bone. The invention also concerns various methods for producing the mould and the pore-forming phase which respectively define the geometry and the porous architecture of the substitute during the forming by cast moulding or injecting of a phosphocalcic paste.

Description

bone substitute calcium phosphate

Field of the Invention

The present invention relates to a bone substitute anatomically shaped and controlled macroporosity made from calcium phosphate materials chemically consolidated cementitious. The substitute may be obtained by forming a liquid or plastic paste composed of calcium phosphate and other sparingly soluble calcium salts. The molding formatting used with a paste and ex vivo chemical consolidation provides the one hand; a more or less large substitute whose controllable anatomical shape corresponds to that of the bone block to be replaced; secondly a macroporous architecture adapted that promotes ingrowth and resorption of the substitute, while ensuring the best initial mechanical properties and their maintenance until the final replacement by new bone graft. The invention also relates to various methods for producing mold and the porogenic phase which define the geometry and the macroporous architecture of the substitute at the casting by shaping or by injection of a calcium phosphate paste.

This type of substitute can be used as artificial bone graft (resorbable object) or as bone implant (nonabsorbable object), and this in a wide range of applications due to its composition and macroscopic characteristics (size, anatomically shaped ) and microscopic (porous architecture, microporosity) perfectly adaptable. It can also be used to support the culture of bone cells in vitro.

State of the art

As part of the repair and replacement of hard tissues of the skeleton, surgeons in orthopedics and traumatology are increasingly encouraged to seek new synthetic materials that can advantageously replace conventional bone grafts. Indeed, the scope autografts bone substitutes is limited to small-sized fillers; allografts can lead to immunological tolerance problems (viral disease transmission) and legislation; bone xenografts are sometimes accompanied by risk of infectious transmission. Therefore, studies have been conducted on synthetic materials of calcium phosphate whose chemical composition is very similar to the mineral phase of bone which makes them perfectly biocompatible. Moreover, unlike the inert biomaterials such as alumina, are bioactive and osteoconductive ie they promote exchanges between the cells and the bone tissue recipient and osteogenesis. These calcium phosphate materials are mainly in the form of ceramics or cements.

There are three main compositions of bioceramics (de Groot et al. 1983). The HAp ceramics are slightly absorbable organic website (jarcho et al. 1981). The β-TCP ceramics are more soluble and resorption in contact with biological fluids has been demonstrated (Eggli et al. 1988). Finally, there bioceramics biphasic, mixtures of HAp and β- TCP whose intermediate properties vary depending on the proportions of the two constituents of the mixture (LeGeros et al. 1988). The biological behavior of bioceramics, especially biodegradation, depends on the physico-chemical characteristics of the biomaterial (mainly Ca / P ratio). It was also shown that the introduction of macropores accelerates substitute recolonization process by the adjacent bone regrowth and new bone. Moreover, it seems that the size of the macropores and the size and number of interconnections between the macropores strongly influence bone ingrowth process (Fabbri et al. 1994). Thus, many methods have been studied to synthesize macroporous bioceramics more or less controlled architecture. Typically, the macroporous ceramic are formed by addition of blowing agents (naphthalene particles, camphor, polyethylene, PVB ...) upon casting by shaping slip or dry pressing (Jarco et al 1981;. Driskell et al. 1973). These pore-forming particles decompose before densification leaving their marks in the form of pores in the ceramic. For his part, White and Schors (1986) developed a method for using coral as blowing. Other techniques, such as those described in European Patent Application EP-A-253506 or WO 98/38949, are also possible. It is also possible to cause exchange between the ion CO32- coral and PO ^ ions "of a phosphate solution at high pressure and high temperature. The ceramic obtained has the crystal structure of HAp and architecture porous coral. However, it is noted that the calcium phosphate ceramics remain biologically less active because of their way of consolidation by high temperature sintering. it is therefore essential to introduce a high pore volume fraction to accelerate significantly ingrowth process and especially bioresorption. in addition, conventional shaping methods do not allow to make ceramics which macroporous architecture is controllable at will. Indeed, it is often difficult to independently determine the volume fraction and the geometry of the macroporosity. This is illustrated particularly in the method using as agents po geneous naphthalene balls. In this case, it is necessary to introduce a very important macroporous volume for interconnections between the macropores, the number and size allow bone ingrowth. All this results in greatly reducing the mechanical properties of macroporous parts. Thus, clinical applications for which this type of transplant would suffer significant mechanical loads are not recommended.

The calcium phosphate materials also in the form of cement. The most commonly studied formulations are: mixtures of tetracalcium phosphate (TTCP) and dicalcium phosphate dihydrate (DCPD) (BoneSource ® HA surround), phosphate mixtures tricalcique- (α-TCP) of monocalcium phosphate monohydrate (MCPM) and calcium carbonate (Norian SRS ®), those of calcium carbonate and dibasic calcium phosphate anhydrous (DCP) and finally mixtures of β-tricalcium phosphate (β- TCP) and MCPM (Mirtchi AA, J. Lemaitre, & N. Terao, Biomaterials, 1989). Their absorbability and osteoconductive nature makes them promising materials for artificial bone graft. Hydraulic calcium phosphate cements are either employed as an injectable paste for temporary bone filling as part of surgical mini- invasive procedures; is used as a bone graft in the form of precured ex vivo parts. Their mode of chemical consolidation at low temperature, that is to say less than 900 ° C, allows to obtain more biologically active substitutes as ceramics of similar compositions consolidated by high temperature sintering. Indeed, these materials retain a higher intrinsic microporosity gives them bioactivity than those bioceramics. However, their low compactness reduces their mechanical properties.

US-A-5714103 patent describes items that can be used as bone implants based on calcium phosphate cement. It consists of a plurality of layers which are progressively superimposed during the production of the object. Here, the macroporosity of the object resembles the natural cancellous bone architecture.

The calcium phosphate cement objects of the state of the art, however, have several disadvantages. In particular, their macroporosity can not be controlled precisely enough.

Description of the Invention

The present invention particularly has the merit of addressing the above problem. It relates to a bone substitute anatomically shaped and controlled porous architecture obtained from calcium phosphate cement materials as well as various processes for its re realization.

Specifically, the substitute according to the invention is characterized in that it comprises at least one elongate gap and of constant cross section, such as a channel, making it possible to precisely control the macroporosity of the substitute. The shaping can be done either by pouring a slurry, or by injection of a plastic paste in a suitable mold. The paste is composed mainly of a mixture of calcium phosphates which can be added other sparingly soluble calcium salts and various inorganic or organic additives setting regulators, deflocculants, plasticizers. Particular care is taken when preparing the dough to get the flowability and wettability properties necessary for good molding. The mold for defining the anatomical geometry of the substitute may be achieved either by siiicone rubber or plaster with a against mold, or using conventional methods of rapid prototyping. Furthermore, different techniques can generate when formatting a controllable porous architecture will, calculated to promote the ingrowth and resorption of the substitute, while ensuring the best initial mechanical properties and their maintenance over time. The pore-forming phase which defines the macroporous architecture to be introduced can be obtained, for example, using son polymers in the simplest case or with the aid of rapid prototyping methods for more complex geometries. A judicious choice of the cement paste formulation helps maintain dimensional changes occurring during the chemical consolidation to a negligible level, allowing to manufacture parts directly to exact dimensions. In addition, this chemically consolidation mode provides biologically active parts. These alternatives can be used as artificial bone grafts in a wide range of applications because of their compositions and their macroscopic characteristics (size, anatomic shape) and microscopic (porous architecture, microporosity) perfectly adaptable.

The substitute calcium phosphate cement can be formed from a liquid or plastic paste composed of calcium phosphate and other sparingly soluble calcium salts, which may be added various inorganic or organic additives (setting regulators, deflocculants, plasticizers ). The principle consists of an aqueous medium a mixture of two co-reactive powders, one acid and one basic, which causes the dissolution of the two reactants and the precipitation of a new thermodynamically more stable phase. In the context of this invention, various known formulations of calcium phosphate cements can be considered. For example, brushite type cements obtained from mixtures of β-tricalcium phosphate and monocalcium phosphate monohydrate rapidly consolidating at room temperature and have a high absorbability (Mirtchi AA, J. Lemaitre, and N. Terao, Biomaterials, 1989) . Furthermore, a new hydroxyapatite cement, obtained by baking in an atmosphere saturated with moisture monetite mixture (dicalcium phosphate anhydrous) and calcium carbonate (calcite, aragonite or vaterite), has been specifically developed for this invention. This cement is particularly suitable for producing substitutes by slurry casting from molds and blowing phases obtained by rapid prototyping methods (see Example 2.2). Other previously known formulations (Norian SRS ®, BoneSource ® surround HA, α-BSM ™ Etex Corporation, CEMENTEK Teknimed ®, ...) are also used in the context of this invention.

The substitute subject of the present invention has a controlled anatomical shape with a very precise definition of the dimensions. The size of the substitute can vary from a few millimeters to several tens of centimeters. Its shape is designed to replicate the anatomy of the bone to be replaced; she especially uses the same external dimensions, facilitating its integration into the recipient site. For example, in the case of long bones such as bone diaphyses, a central channel heralding the medullary canal may be provided along the axis of substitute, with the aim of accelerating vascularization Block after substitution.

The porous architecture substitute may comprise a core network of open pores in elongated form (channels) which may be added as appropriate, one or two secondary porous interconnected networks to the first network. Mainline elongate pores can be a square or random network type, preferably hexagonal. It can be oriented at will, for example, parallel to the main mechanical stress that has to bear the substitute: this allows to optimize the mechanical performance of the object. The pores of the core network are in the form of parallel elongate channels therebetween. For example, these channels can be approximately cylindrical. The intersection of these elongate channels with a plane perpendicular to their direction form constant surface sections whose centers of inertia are spaced from 0.6 to 2 mm preferably. The constant section of the channels has a perimeter which presents itself generally in the form of an approximately circular convex closed curve. The area occupied by the constant section of the channels is between 8 10 "3 to 0.8 mm 2, preferably between 0.1 and 0.3 mm 2. One or two networks of secondary pores connect the elongated pores of the core network to facilitate metabolic exchange between the substitute and the physiological environment. They are in the form of holes can be of cylindrical shape, whose section is constant between 10 3 "3 and 8 10 contained" 32 mm. pore constant sections inertial centers can be within 1.1 to 2.1 mm preferably. the interconnected macroporous architecture as the case occupies a volume fraction between 10 and 70%, preferably between 30 and 60% of the total apparent volume. in addition, in addition to that -ci intrinsic microporosity of calcium phosphate cement which occupies according to the formulation approximately 20-60% of the total volume. ultimately, the substitute has a total porosity between 28 and 88% by volume.

The realization of the substitute is ex vivo. According to a preferred embodiment of the invention, first of all, the preparation of the dough (plastic or liquid) containing the co-reactive powders is the subject of particular care in order to obtain flowability properties and wettability necessary for a good casting. As applicable, the rheology and consistency of the pulp can be optimized by the addition of water-soluble polymers preferably biocompatible (polyacrylic acid, etc.). Different treatments are also used to grind or deagglomerate co-reactive powders to better disperse and homogenize and pasta.

Formatting substitute is made by casting or by injection in a mold. According to the desired anatomical shape, there are various methods for obtaining the mold in which is cast or injected cement paste. For simple geometries, the molds can be made directly in silicone rubber or plaster from a previously machined steel against mold. It is also possible to manufacture molds of complex geometry using a prototyping process. The rapid prototyping process by type wax jet ModelMaker II marketed by Sanders Prototype Inc., USA, is particularly suitable. In this case, the shape of the mold is designed from images in three dimensions defined by CAD software or directly from scanned images. The data transfer software enslaving the prototyping machine can be in any known format, for example, .IGES, STL, DXF, .HPP, .OBJ. The software uses the information to control a jet of wax in the horizontal plane to make the mold with successive layers. The pore-forming phase to generate the final macroporosity, can be performed directly in polymer yarn for simple architectures or rapid prototyping method for more complex macroporous architectures. In the latter case, the pore-forming phase is carried out simultaneously with the mold and is integrated thereto.

After molding, the ex vivo parts consolidation occurs by chemical reaction at temperatures which may vary preferably between room temperature and 121 C C. The release step can be performed before or after chemical consolidation, depending on the formulation cement and nature of the blowing and molding materials. Finally, the pore-forming phase may be removed either by simple mechanical extraction (son case of polymers) by thermal decomposition at a temperature below 900 ° C, chemical attack or dissolution in a suitable solvent.

The benefits of an anatomical substitute controlled macroporous architecture are numerous. First, because its characteristics (composition, shape, macroporosity) is perfectly controlled and optimized mechanical held, the substitute can be used as synthetic bone substitute in many clinical applications. It is possible to produce parts with the geometry and macroporosity are optimized so as to obtain mechanical properties close to those of the bone to be replaced, in particular the elastic modulus, while promoting resorption and rapid recolonization by bone tissue new. We can consider its use as macrogreffe in cases, for example, extension or replacement of long bones or lumbar fusion for which transplantation is rapidly withstand high mechanical loads.

The substitute can also be used after culturing medium of bone cells in vitro. This step of initiating the re-colonization of macroporous architecture and microporosity by bone tissue to préconsolider the room before implantation in a biological medium. The culture medium may contain various active molecules, such as antibiotics or bone growth factors (Bone Morphological Proteins) in order to stimulate the proliferation of bone cells in the heart of the substitute. It is also possible to use the substitute as simple culture medium of bone cells.

Unlike injectable cement, the material is pre-cured ex vivo. Under these conditions, it is possible to control at will the characteristics of substitute ie: its anatomical shape, using a mold geometry more or less easy to realize complex; its porous architecture, by introducing a blowing phase defined and optimized architecture. The chemical consolidation step unlike the sintering of ceramics, is carried out at low temperature and does not cause a substantial change in dimensions of the part. The shape and porous architecture of the substitute are well defined from the mold and do not change during consolidation. In addition, the chemical consolidation method gives the substitute highly bioactive character unlike similar compositions consolidated by high temperature sintering. The substitute retains a significant microporosity which promotes bioresorption and allows its impregnation with various active molecules (antibiotics, bone growth factors ...). It is therefore not necessary to introduce a significant macroporosity to significantly improve bone ingrowth material which minimizes mechanical weakening substitute. Formatting Techniques developed for this type of substitute used to generate a porous architecture perfectly controlled and optimized on the biomechanical and biological. For example, the porous core network can be oriented parallel to the mechanical stresses undergone by the substitute, once in place, which improves the initial mechanical strength of the assembly. Moreover, the substitute may have a totally interconnected macroporous, supports rapid bone recolonization, despite low pore volume fraction. This guarantees high mechanical properties unlike conventional macroporous ceramic substitutes for whom finding a sufficient interconnection between pores requires a large total pore fraction often around 70%. Moreover, the macroporosity is studied so as to accelerate the ingrowth of the graft before bioresorption process involved. This allows a fast mechanical reinforcement by new bone and a good maintenance of the functional properties of the graft within the first weeks after the introduction of the substitute. Thus, this macroporosity reduced with optimized geometry promotes rapid bone ingrowth without sacrificing significantly the mechanical substitute.

Moreover, the various processes used for making molds and blowing phases, for example a silicone rubber mold or plaster and a pore-forming phase polymer thread or with a rapid prototyping, it possible to obtain geometries and porous architectures controllable at will. More particularly, the method by rapid prototyping by spray wax has several advantages. First, the design of parts (pore-forming phase and mold) is aided thereby improve the speed and flexibility: for example, the anatomic shape can be defined from digital medical images and 'interconnected macroporous architecture can be modeled to optimize simultaneously the final mechanical properties of the substitute and bone recolonization. In addition, this method allows for very complex shapes with high dimensional accuracy. The invention is illustrated hereinafter by means of the following figures: Figure 1 shows a bone substitute according to a first embodiment of the invention. Figure 2 shows the substitute of Figure 1 viewed from above and a cutting face.

3 illustrates a mold for producing the bone substitute of Figures 1 and 2. Figure 4 shows part of the device for carrying out the macroporosity of the substitute of the preceding figures. Figure 5 shows the other part of the same device. 6 illustrates all of the same device seen in perspective. 7 shows the same device with polymer son. Figure 8 shows the same assembly in a position with the mold of the preceding Figures. Figure 9 shows the assembly of Figure 8 in another position with the implant.

Figure 10 shows a bone substitute according to a second embodiment of the invention. Figure 1 1 shows the substitute of Figure 10 from above and a cutting face. 12 illustrates a mold for producing the bone substitute of Figures 10 and 11. Figure 13 shows the same mold in a perspective view. Figure 14 shows the assembly formed by the mold and the device for performing the macroporosity of the alternative of Figures 10 and January 1.

EXAMPLE 1 SUBSTITUTE PARALLEL ARCHITECTURE

Macroporous WAY WAY OR MADE FROM CEMENT TYPE brushite.

The substitute is made from injection as a liquid pulp brushite cement in a silicone rubber mold (unidirectional macroporosity) or stainless steel (bidirectional macroporosity). The macroporous architecture is made by molding from son polymer (eg. Ex. Nylon) or stainless steel (bidirectional). a) Substitute unidirectional macroporous architecture.

substitute description (fig. 1 and 2) The substitute is in the form of a cylinder 10 mm in diameter and 10 mm in height. A central channel (1) of 2 mm diameter is performed along the axis of substitute and simulates the medullary cavity of the bone to be replaced. The macroporous architecture consists of a main hexagonal array of cylindrical pores (2) parallel to each other. These macropores have a diameter of 0.5 mm and have their axes of symmetry remote 1.5 mm. The macroporous architecture of the hexagonal type occupies 9 to 10% of the total apparent volume outside center channel. The formulation of brushite cement used has an intrinsic microporosity which occupies about 31% of the total volume excluding macroporosity. The substitute has a total porosity of about 37 to 38% by volume.

Description of the elements of the device (fig. 3, 4 and 5) The mold (3) is constructed in one piece of silicone rubber by simply casting in a steel against mold. It comprises two openings of different diameters (4, 5) and a side slot (6) (fig. 3). The device used to perform the unidirectional macroporosity consists of two aluminum parts (fig. 4 and 5) both previously drilled 36 holes (7) of 0.6 mm in diameter and whose center of symmetry are spaced 1.5 mm. It is through these holes that pass the wire strands of polymer, 0.5 mm diameter and 40 mm long. A rod (9) 2 mm in diameter is fixed in the lower plate (8) while the upper plate ^ 0) has a central orifice (11) of 2.1 mm in diameter (fig. 4 and 5).

Œuyre setting of the device (fig. 6, 7 and 8) The device for generating the macroporosity is designed to be reusable. The plate (10) with the central orifice slide along the rod (9) attached to the second plate (8) (fig. 6). The polymer strands of 40 mm length are threaded through holes 36 (7) of 0.6 mm in diameter of the two plates (8, 10). These strands are then fixed to the plate (8) by gluing. And the plate (10) remains mobile and can slide along the rod and son network. The polymer strands (12) are tensioned between the two plates to form a unidirectional network son. Their ends on the side of the movable plate (10) are immersed in a small liquid wax container. Once hardened, the wax (13) keeps the son parallel (Fig. 7). The movable plate (10) is moved along the rod (9) and son (12) to join the plate (8) fixed. Thus, the son network (12) is held by the two plates (8, 10) at one end and by the hardened wax (13) at the other end (Fig. 8). The son network is inserted into the silicone rubber mold (3) through the slot (6) formed on the side of the mold (fig. 8). The whole is then centered relative to the mold axis: the plate (10) is engaged in the bottom opening (5) of the silicone rubber mold provided for this effect (Fig. 8).

Synthesis and molding brushite cement paste in the mold The system combines two calcium phosphate powders and water corresponds to the following reaction:

This precipitation reaction of the brushite in the presence of water gives rise to the cement. In the absence of additives, this reaction is fast and the cement hardens in less than a minute, which makes its use impractical. The use of a dilute solution of H 2 SO 4 (0.1 M) as a combined mixing solution to a specific dosage of additives (pyrophosphate) allows good control of the cement setting time. The setting time is adjusted here between 10 and 15 minutes to facilitate the implementation.

The solid / liquid mixture is set at 2.5 g / ml to obtain a plastic paste viscosity suitable for good molding. The mixture consists of: - 1.2 g of tricalcium phosphate powder beta (β-TCP) whose Ca / P ratio is between 1.44 and 1.47. The median diameter of this powder was 2.5 .mu.m and the specific surface area of about 1.5 m 2 / g.

The sulfuric acid and the powders of MCPM and Na 2 H 2 P 2 O 7 are carefully mixed in a mortar with a spatula. The β-TCP powder is then added and the mixture is blended about one minute until a homogeneous paste. It should be noted that at room temperature (19-20 ° C), the pulp must be used within 10 minutes.

The dough is placed in a syringe and injected into the silicone rubber mold through the top opening (4). This step is done several times to ensure good filling of the mold. Between two successive additions, the mold is vibrated about 30 seconds to remove any air bubbles which might remain in the pulp. The mold is filled to the brim.

Demolding substitute (fig. 9)

Once consolidation is complete cement, the substitute is removed silicone rubber mold through the slit (6). The wax part (13) is removed, thus releasing the ends of the wire strands of polymer. Finally, the polymer strands of wire and the central rod are carefully removed from the alternative by simply pulling on the base (8) keeping the plate (10) fixed (Fig. 9). The height of the substitute is adjusted to 10 mm by polishing

b) Substitute bidirectional macroporous architecture.

substitute Description (fig. 10 and 11)

The substitute is in the form of a cylinder 10 mm in diameter and 10 mm in height. A central channel (14) of 2 mm diameter is performed along the axis of substitute and simulates the medullary cavity of the bone to be replaced. The macroporous architecture consists of two elongated pores interconnected networks. The main porous network (15) of hexagonal type is identical to that substitutes for unidirectional macroporous architecture. It consists of parallel cylindrical pores each having a diameter equal to 0.5 mm and whose axes of symmetry are spaced 1.5 mm. The cylindrical macropores of the secondary network (16) have a diameter of 0.3 mm. Their axes of symmetry are spaced 2 mm along the axis of substitute and 1.3 mm depending on the planes perpendicular to this axis (section AA 'of Figure 11). The secondary pore network does not pass through the central channel (14) and split share is both sides thereof. The total macroporous architecture occupies a volume fraction of 10.2%. The formulation of brushite cement used has an intrinsic microporosity which occupies about 31% of total volume. The substitute has a total porosity of about 38% by volume.

(Fig. 4, 5, 12, 13 and 14) (fig. 12) Description of the elements of the device The mold stainless steel is composed of four parts: two half-discs (17.1 and 17.2) which put together form a base (17) of 30 mm in diameter and 2.5 mm thickness in which is made a central hole of 10 mm in diameter; two half-cylinders (18.1 and 18.2) attached to each hollow half a base. Each assembly (half-disc more half-base) form a half-mold of stainless steel. The thus assembled mold therefore comprises a base (17) provided with a hollow cylinder (18) of height equal to 14.5 mm, internal diameter equal to 10 mm and whose wall thickness is 1 mm. The hollow cylinder (18) composed of two half-cylinders (18.1 and 18.2) is pierced right through 24 spherical holes (19) of 0.35 mm in diameter (fig. 12 and 13). These holes have their axes of symmetry spaced 2 mm along the axis of the cylinder and of 1.3 mm according to planes perpendicular to this axis. The device used to perform the macroporosity of the core network is identical to that implemented in the case of alternative unidirectional macroporous architecture (see below and Fig. 4 and 5). It consists of two aluminum pieces 36 pierced by holes (7) of 0.6 mm in diameter, the centers of symmetry are spaced 1.5 mm and through which pass the polymer strands of 0.5 mm diameter and 40 mm long. A rod (9) 2 mm in diameter is fixed in the lower plate (8) while the upper plate (10) has a central orifice (11) of 2.1 mm in diameter. Œuyre setting of the device (fig. 6, 7 and 14) The first implementation step corresponds to that used for the substitutes unidirectional macroporous architecture (see above and Fig. 6, 7). The unidirectional son network for generating the main macroporous network is inserted between two stainless steel mold halves. The whole is then centered relative to the mold axis: the plate (10) is engaged in the lower opening of the stainless steel mold provided for this purpose.

The additional step is to pass stainless steel wire strands (20) of 0.3 mm in diameter and 30 mm in length through the 24 channels (19) of stainless steel mold (21) (fig. 14 ). The whole forms a second steel son network (20) interconnected and perpendicular to the main network polymer son (12). Each steel wire comes into contact with polymer son of each row of the first core network.

Synthesis and molding brushite cement paste into the mold These two steps are similar to those used for the substitutes unidirectional macroporous architecture already described.

Divesting substitute Once completed the consolidation of cement, wire strands of stainless steel (20) are removed one by one from the group consisting of the mold and substitute. The two stainless steel half molds are removed releasing the substitute. The wax part (13) is removed, thus releasing the ends of the wire strands of polymer. Finally, the polymer strands of wire and the central rod are carefully removed from the alternative by simply pulling on the base (8) keeping the plate (10) fixed. The height of the substitute is adjusted to 10 mm by polishing. Example 2: SUBSTITUTE CEMENT phosphocalcium ANATOMICAL FORM AND ARCHITECTURAL Macroporous MADE FROM PROCESS PROTYPAGE QUICK JET WAX (MODELMAKERII UNIT PROTOTYPE TYPE SANDERS INC..).

Depending on the case, the shape of the piece of wax produced by rapid prototyping is either the positive or the negative of the anatomic shape of the substitute. The pore-forming phase is also produced by rapid prototyping always corresponds to the negative of the desired macroporous architecture substitute. The design of the mold geometry and pore-forming phase can be scanned by imaging or from CAD software. The macroporous architecture can be complex, for example consist of a three-dimensional network of interconnected cylinders. Moreover, it is possible to model the interconnected macroporous architecture to adapt substitute mechanical properties while promoting her bone recolonization. It is also possible to introduce a central channel that simulates the medullary cavity of the bone to be replaced in the case of long bones.

a) Substitute in brushite cement.

A piece of wax is performed by rapid prototyping jet wax. Its geometry corresponds to the negative of the anatomic shape and macroporous architecture substitute. Thus, the wax part plays two roles: first, it defines the outer geometry of the substitute; secondly, it serves phase porogen that is to say that once removed, it leaves an imprint in the concrete corresponding to the desired macroporous architecture. An upper opening is provided at the part design to permit its injection by filling the dough into brushite cement. The steps of brushite cement paste synthesis and filling the wax part are similar to those of Example 1 described above. Once the chemical consolidation of the finished cement, the wax is eliminated at low temperature by dissolution with a solvent. The deputy obtained brushite cement has an anatomic shape and macroporous architecture controlled at will. b) Substituted hydroxyapatite cement.

The substitute is shaped by casting a calcium phosphate slurry in a plaster mold. Two plaster mold halves are made using the method of the lost wax mold. To do so, two parts corresponding to the positive wax of two half-substitutes are produced by rapid prototyping jet wax. These two pieces are then immersed separately in liquid plaster: after consolidation of gypsum, wax parts are removed using a solvent which allows to obtain the two half plaster molds. A third piece of wax is produced by prototyping jet wax. The geometry corresponds to the negative of the macroporous architecture of the substitute and was designed to fit perfectly into the mold formed by the two plaster mold halves. The device obtained (two plaster half-molds and blowing phase) serves for the production of substitute from casting a calcium phosphate slurry. This slurry is composed of a stoichiometric mixture of anhydrous dicalcium phosphate powders (DCP) and calcite (CC) in the presence of a dispersant solution of polyacrylic acid to 2 wt% and at a rate of 0.5 ml per gram of mixture powder (DCP / DC). A continuous supply of slurry into the device to control the height of the workpiece as and the shrinkage due to ressuyage by plaster. Once the consolidated green body, the plaster mold is removed and the pore-forming phase wax is removed at low temperature using a solvent. The green body is then processed in an autoclave. Consolidating reaction occurs at 121 ° C for 1 hour and results in the precipitation of hydroxyapatite accompanied by a release of carbon dioxide and water:

Claims

1. Bone substitute, made in one piece from cementitious calcium phosphate materials chemically consolidated at low temperature and in the presence of water, characterized in that it comprises at least one interstice (2,15,16) of elongate shape and of substantially constant section.

2. Bone substitute according to the preceding claim, characterized in that the one or more gaps (2,15,16) are aligned parallel to the main mechanical stresses to be borne by the substitute, once in place in a physiological medium.

3. Bone substitute according to claim 1 or 2, characterized in that it comprises at least one main array of parallel channels (15).

4. Bone substitute according to the preceding claim, characterized in that it comprises at least one secondary network of channels (16) which preferably connect the channels (15) of the main network.

5. Bone substitute according to claim 3 or 4, characterized in that the channel section (15) of the main network is between 8.

10 -3 and 0.8 mm 2, preferably between 0.1 and 0.3 mm 2.

6. Bone substitute according to claim 4 or 5, characterized in that the channel section (16) of the secondary network is comprised between 3.10 -3 and 8. 10- 3 mm 2.

7. Bone substitute according to any one of the preceding claims, characterized in that the volume fraction of or gaps (2,15,16) is between 10% and 70% and preferably between 30% and 60%.

8. Bone substitute according to any one of the preceding claims, characterized in that the total porosity of the substitute is between 28% and 88%.

9. Cement for bone substitute according to any preceding claim made from a liquid or plastic paste comprising one or more calcium phosphates and at least one other sparingly soluble calcium salt such as sulfate, pyrophosphate or carbonate.

11. Cement for hydroxyapatite bone substitute according to any one of the preceding claims obtained by baking in an atmosphere saturated monetite mixture of moisture (dicalcium phosphate anhydrous) and calcium carbonate (calcite, aragonite or vaterite).

12. A process for obtaining a bone substitute according to any one of the preceding claims, characterized in that the cement in the consolidation reaction is chemically ex-vivo or in temperature and ambient medium or in water-saturated medium and at elevated temperature.

13. A process for obtaining a bone substitute according to any one of the preceding claims, characterized in that the anatomical geometry and the macroporous architecture are conducted during the shaping by molding the calcium phosphate paste and chemical consolidation ex -vivo.

14. A process for obtaining a bone substitute according to any one of the preceding claims, characterized in that the one or more gaps (2,15,16) are made using polymer son (12) such as nylon PVB or polyethylene.

15. A process for obtaining a bone substitute according to any one of the preceding claims, characterized by the use of a rapid prototyping method such as stereolithography or rapid prototyping by spray wax, for carrying out the mold and the porogenic phase.